This disclosure relates to X-ray imaging systems, and, in particular, to X-ray imaging systems employing optic devices to produce X-ray beams having desired spectral shape and properties.
Conventional laboratory sources produce a large cone of X rays, the majority of which typically are not utilized to analyze a sample in an X-ray system. X-ray optics may be used to redirect some of these unused X rays into useful directions. However, the efficiency of redirection decreases with increasing distance between the X-ray generation point inside the X-ray source and the collecting/redirecting optic(s). This decrease is typically due to the decrease in X-ray intensity with increasing distance between the X-ray generation point and the optics. Specifically, the X-ray intensity decreases as the square of the distance between the optics and X-ray generation point. Additional issues with respect to an X-ray source point and optics arrangement include: alignment of the optics and the X-ray generation point, and drifting of the X-ray beam generation point due to target heating or lack of dynamic electron beam control.
The optimal position for disposing the optic to obtain maximum X-ray intensity would be at the X-ray generation point, however, with commercially available optics such as polycapillary optics or the singly- or doubly-curved diffractive optics such an arrangement is not feasible. Currently, polycapillary and multilayer diffractive optics are the only commercially available optics that collect a reasonable source solid angle and redirect the X rays into usable directions. The polycapillary channel size is too large to utilize small source spots, e.g. nanometer to micron-sized focal spots. Due to its large size, the polycapillary optics needs to be placed several hundred microns to centimeters away from the X-ray generation point. This large distance between the optics and the X-ray generation point reduces the intensity of the output X-ray beam that comes out of the optics. For both singly and/or doubly curved diffractive optics, the optics are typically placed at distances on the order of centimeters from the X-ray generation point to reduce the strain in the optics, which makes the optics difficult to manufacture and reduces the optic output beam quality. In addition to reducing the X-ray intensity, placing the optic at a large distance away from the X-ray generation point also reduces the robustness of the optic alignment with the X-ray generation point. Lastly, polycapillary optics are limited to transmitting X rays below 60 keV, which prevents them from being used in a number of non-destructive testing (NDT) imaging applications, e.g. computed tomography (CT) of electronic circuit boards.
It would thus be desirable to dispose the optic device on the X-ray generation point so as to obtain optimal X-ray intensity, and to address alignment issues between the optic device and the target.